1. Field of the Invention
This invention relates to routing a telephone call to an alternate termination when the call cannot be completed to an originally selected termination.
2. Background Information
Many businesses desire that calls which cannot be completed to their intended terminations be rerouted to a secondary or alternate termination. Calls may fail to complete for a variety of reasons. For example, the intended termination may refuse the call or may be unable to accept it. A customer dialing an 800 number might initially be routed to an understaffed call center. Rather than have the customer receive a poor grade of service, such as an unacceptably long wait, the call center manager may prefer to redirect the call to a secondary termination which may be able to provide a higher grade of service.
A typical prior art telephone network 100, which provides call redirection, is shown in FIG. 1, as having three network switches 102, 104 and 106 are connected by trunks 122, 124 and 126. Each switch 102, 104 and 106 may also be connected to one or more local exchange networks (LEN) and/or one or more customer premise equipment (CPE), represented by blocks 110, 112 and 114, respectively. Each LEN/CPE is connected to one or more terminations, such as standard telephones or private branch exchanges (PBX), represented by blocks 111, 113 and 115, respectively. Each switch is also communicatively coupled to at least one network database 108 over signaling network 128.
Network 100 is exemplified by U.S. Pat. No. 5,369,695 to Chakravarti et al. In Chakravarti et al., a telephone network switch 102 is arranged so that after forwarding an incoming call from LEN/CPE 110 to an intended terminating switch 104, switch 102 responds to any one of a number of conditions requiring redirection of the call by redirecting the call to an alternate termination, switch 106, identified as a function of a redirect code derived from associated calling information. Such conditions include the case of ring no answer and the case in which an answering party requests such redirection. The switch obtains the redirection code from a centralized network database 108 which derives the redirection code from calling information supplied by the switch.
Chakravarti et al. describes call redirection in response to three conditions: ring no answer, busy and post ringing redirection request. However, call redirection may be desired in response to any condition which prevents call completion. Examples of such conditions are: network congestion, transmission line outage, switch failure and LEN or CPE inability to complete the call. Chakravarti et al. does not deal with these conditions. In addition, Chakravarti et al. describes performing the same call redirection in response to all three conditions. It is desirable to vary the redirection performed depending upon the condition encountered.
Another typical prior art redirection scheme is described in U.S. Pat. No. 5,253,288 to Frey et al. In Frey et al., a call from originator 111 is initially extended through a toll network 100 toward the first destination 113; if the toll network 100 is congested and cannot reach an egress switch 104 to access the first destination 113 or if a local exchange network 112 connecting the first destination 113 to the toll network 100 is congested, or if a first destination PBX 113 cannot be reached from the toll or local network because all access channels thereto are blocked, or if the first destination PBX 113 is congested or attendants are unavailable, an indication that the call cannot be completed to the first destination 113 is sent back to the ingress switch 102 of the toll network for that call. The call is then redirected from the ingress switch 102 of the toll network to an alternate destination 115. If the first choice destination 113 is a PBX and the PBX rejects a call, the reason for the rejection can be used for altering the choice of an alternate destination or for canceling a potential redirection.
Frey et al., describes redirection of calls using tables organized around "non-existent" switch numbers. When a call having an indication that it is to be directed to a non-existent switch enters a switch, the non-existent switch number is translated within the switch to provide the real number of the destination switch. Frey et al., describes providing multiple alternative destinations by using tables to store a plurality of destination entries and incrementing from one table entry to the next. Frey et al. also describes altering the choice of an alternate destination based on the reason a call was rejected, but does not describe a mechanism for accomplishing this. The method described in Frey et al. provides limited flexibility for call redirection.
A need exists for improved control over multiple redirection of calls to upgrade the quality of service currently available to businesses and subscribers.